In short - when material plugins are assigned on object and have non-zero Repetitions U or Repetitions V in their texture tag assignment, the editor preview does not clip the preview image at all. I noticed this only for Cinema 4D S22 and above.
Some details - I have a material plugin deriving from the MaterialData class, with an override for MaterialData::InitGLImage(..) to generate a generic preview for the material in the editor. Until S22, the editor preview correctly showed the material with the specified repetitions in the TextureTag. After that only the native materials seem to show this correctly.
Is there a flag that we missed adding for S22 or something else that was introduced and is missing on our side, or this is a problem in Cinema 4D?
I did reproduced the issue, with the s22 we changed the viewport and many changes have been introduce.
I have contacted the devs to have some feedback about that.
This is a bug and will be fix in a futur release.
Unfortunately, there's no workaround.
Thanks for the investigation. At least now we are aware the problem is not on our side.